The present invention relates to a high-purity hafnium material in which the impurity content of Fe, Cr, and Ni, the impurity content of Ca, Na, and K, the impurity content of Al, Co, Cu, Ti, W, and Zn, as well as the alpha dose, the impurity content of U and Th, the impurity content of Pb and Bi, and the content of C as a gas component contained in the hafnium are reduced, as well as to a sputtering target, a gate insulation film and a metal gate thin film, which are formed from such high-purity hafnium material. It also relates to a manufacturing method of high-purity hafnium.
Conventionally, there are numerous documents relating to the manufacture of hafnium. Hafnium is superior in heat resistance and corrosion resistance, and is characterized in that it has a strong affinity with oxygen and nitrogen. In addition, since the oxides or nitrides thereof have superior stability in high temperatures, they are utilized as fire-resistant materials in the manufacture of nuclear ceramics, steels or castings. Further, recently, these are also being used as electronic materials or optical materials.
The manufacturing method of metal hafnium is proposed to be the same as that of metal zirconium. As such examples, there are a method of reacting a fluorine-containing zirconium or hafnium compound with metal aluminum or magnesium in inert gas, reducing gas or a vacuum at a temperature of 400° C. or higher (e.g., refer to Patent Document 1), a manufacturing method commonly adopted in the sealing metals, wherein metals are respectively manufactured by reducing zirconium chloride, hafnium chloride or titanium chloride (e.g., refer to Patent Document 2); a manufacturing method of hafnium or zirconium characterized in the reaction vessel structure upon reducing zirconium tetrachloride or hafnium tetrachloride with magnesium and the manufacturing technique thereof (e.g., refer to Patent Document 3); a method of manufacturing chloro-, bromo- or iodic zirconium, hafnium, tantalum, vanadium and niobium compound with sublimation pressure by introducing these elements into a crucible (e.g., refer to Patent Document 4); a method of refining zirconium or hafnium chloride or an acid chloride aqueous solution with strongly basic anion exchange resin (e.g., refer to Patent Document 5); a method of collecting zirconium via solvent extraction (e.g., refer to Patent Document 6); and a crystal bar hafnium manufacturing device having characteristics in the feed portion (e.g., refer to Patent Document 7).    [Patent Document 1] Japanese Patent Laid-Open Publication No. S60-17027    [Patent Document 2] Japanese Patent Laid-Open Publication No. S61-279641    [Patent Document 3] Japanese Patent Laid-Open Publication No. S62-103328    [Patent Document 4] National Publication of Translated Version H3-501630 (WO89/11449)    [Patent Document 5] Japanese Patent Laid-Open Publication No. H10-204554    [Patent Document 6] Japanese Patent Laid-Open Publication No. S60-255621    [Patent Document 7] Japanese Patent Laid-Open Publication No. S61-242993
As described in the foregoing documents, there are numerous refining methods and extraction methods of hafnium. In recent years, deposition on electronic components using hafnium silicide is being demanded. In particular, usage as a gate insulation film or a metal gate film is being considered. Since these films are located immediately on the Si substrate, the influence of purity is significant. Contamination on the semiconductor substrate is particularly a problem.
Nevertheless, there had been a problem that significant amounts of zirconium are contained in hafnium, and the high purification of hafnium could not have been achieved easily. In addition, when hafnium as an electronic material was used as a gate insulation film or a metal gate film to be disposed in the vicinity of a silicon substrate, since there was no knowledge of what kind of behavior (adverse effect) the impurities contained in hafnium would yield, a problem is that the inclusion of impurities in hafnium has been tacitly accepted.
This is primarily attributed to the fact that the use of hafnium as an electronic component material such as a gate insulation film or a metal gate film is based on very recent technology.